Ask HN: How to Download Linux Mint Kernel Source?

I'm asking here at HN because the Linux Mint forums are useless, no one answers questions at Stackoverflow, and Kuro5hin just makes fun of me whenever I try to ask a serious question.

My specific problem is that I want to build - from source - the exact same kernels as I have on my Linux Mint installation. I'm pretty sure this can be done but I'll be damned if I can find any documentation as to how to do it.

I need this because I'm going to do some rather serious kernel hacking - not device driver work, but in the core of the kernel. What I want to do is to run a bunch of userspace tests on an unpatched kernel, then reboot on my patched kernel then run all those same tests.

I am running Linux Mint 16 Petra Cinnamon 64-Bit in VirtualBox on my MacBook Pro, and 17.1 Cinnamon 64-bit natively as well as in VirtualBox on a homebuilt Xeon box.

   $ cat /etc/apt/sources.list
   #deb cdrom:[Linux Mint 17.1 _Rebecca_ - Release amd64 20141126]/ trusty contrib main non-free

   deb-src http://www.linuxmint.com/ trusty contrib main non-free

   $ sudo apt-get update
   ...
   Err http://www.linuxmint.com trusty/contrib Sources                            
     404  Not Found
   Err http://www.linuxmint.com trusty/main Sources                               
     404  Not Found
   Err http://www.linuxmint.com trusty/non-free Sources                           
     404  Not Found

While it would seem to make sense that the non-free sources aren't posted, I would expect there to be source to at least some of them.

   $ uname -a
   Linux hal9000 3.13.0-37-generic #64-Ubuntu SMP Mon Sep 22 21:28:38 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

Thanks! -- Mike